Too funny to not tell you...

I have a cross beak easter egger and the other chickens are constantly trying to remove the odd thing they see on her beak-that being her lower beak...it is so hilarious when she tries to peck back at them. She puts up with it for a while, as it cleans stuff off her beak that she cannot get off...
This bird is fiercely independent and not growing as fast as the other chicks, so I make her a mash daily with chick starter and oats and yogurt and put her in her special place (formerly known as time out) and give her a bowlful of that mush and she goes to town without the other chooks bothering her---now she's gaining weight!
Gotta love that face!

I don't know the specifics of when you can trim a beak, but I know I've read on here about it before. I have a friend whose chicken could not eat right and wasn't laying due to her crossed beak. She took him to an Ag professor and he trimmed her beak and now she can eat and has started laying eggs. They didnt' think she would because of not being able to eat properly when she was growing.

I would do a search for beak trimming or maybe post a picture of her in the "emergency" section if it seems like she's not able to eat, hopefully someone with more experience might have some advice on whether trimming her beak would help her to eat better on her own.